libext2fs: fix problems with LE<->BE conversions on BE platforms

libext2fs: fix problems with LE<->BE conversions on BE platforms

Fix more problems that I found when testing on ppc64:

- Inode swap cut and paste error leads to immutable inodes being
  detected as inlinedata inodes, leading to e2fsck incorrectly barfing
  on i_block[] contents.

- Superblock csum/verify must be aware of the fs->super byte order
  when checking for metadata_csum feature flag.  (Hint: in _openfs(),
  fs->super is in LE order for the first csum verification)

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>